Radar vs Reality

I'm on Toyos 35/12.5/17

When my speedometer indicates 70mph, Google maps GPS shows 77mph. Speedometer 80, GPS 88.

I've done some 84mi trips per Google maps. My odometer would register 74.x miles. So my odometer is understated by 12%.

 

Who knew that Toyota would be THAT nanny-ish. Up to now, I always thought that the GPS speed, shown, was “off”. (How could Toyota be wrong?) Thank goodness I’m not inclined to hang in the fast lane and drive the speed shown in the cluster.

 

OP, if you’re that concerned about the speed being accurate (not a dig at you - I’m one of those people) you can always get a speedometer calibrator.

I have the hypertech speedometer calibrator because I run 33” tires and my speedo is very accurate.

 

Honestly I was just wondering where everyone was. Meaning how many trucks are high, low, dead nuts on.

 

Well then to answer that question for my truck…my Speedo was a couple MPH off (low) with the OEM tires (245’s).

When I upgraded to 265/75/16 tires, the Speedo was 100% accurate. Now with my 33’s it would be a couple MPHs off in the other direction if I didn’t have the speedo calibrator.

The amount that the Speedo is incorrect also varies by speed. It will be more inaccurate at higher speeds, if it’s not accurate.

 

You guys worry about speed limits?

The rules are made up guys, that's all. Most are unnecessary.

 

Twenty five mph is slow enough that variances between the street radar unit and your speedometer may not show. Get to highway speeds and you'll start to notice a discrepancy. I know my motorcycle reads about 1.5 mph fast from actual GPS at normal speeds but past triple digits the variance increases. Phone "GPS" don't actually use satellites; but calculates location via cell towers so it's not as accurate as a true satellite based GPS.

Like any instrument they're as accurate as how they're set. The radars in our patrol cars rarely get out of calibration despite living in a bumpy environment that's exposed to temperature variances. If so they need to go back to the factory as they don't get "calibrated" by the end user. However the calibration is easily confirmed by the officer regularly with tools.

So in a nutshell, factory speedometers aren't as accurate as radar or GPS but close enough.

 

Well gps for civilians is def not as accurate as it could be.

 

Did this, updated my phone and all apps. Still doesn’t display a speedo. Now I just feel old.

 

I have an Apple.
I just pulled those directions off of Google.

Pretty sure Waze does speed too.
I'll have to take a look next time I drive.

 

Just went down the road and checked.
Waze does show real time speed.

 

My truck's indicated speed was dead on from the factory, unlike some others here on this forum. Increased the tire size and had to interpret, then put in a speedometer calculator correction and was pleasantly surprised as to the returned accuracy. Had to fiddle with the settings of the Hypertech quite a bit to my satisfaction. Should have done it years ago, but at that time the cruise control display was not corrected. If you do go to a Hypertech unit leave the programming cable attached and available below the dash for future programming.

 

Are you sure it was the speed that was correct from factory and not the odometer? From the factory, in every truck I’ve ever been around, the speed reads fast by a few mph at highway speed, but the odometer is spot on so as to not speed up warranty.

Tested this in numerous trucks and all are identical in my testing.

 

I use a 10-year-old portable Garmin GPS. At least I can take it with me if I god-forbid must abandon the truck or if I rent a vehicle. Before changing shoes to Falken AT4 analog speedometer match it enough I did not notice. Now the analog speed is 2 MPH below the GPS.

 

Positive as to the speedometer, collaborated by two GPSs; I pay no attention to the odometer. I took notice because it was accurate, unlike all previous vehicles I have had.

 

Pics of the Trans Am, please.

 

Radar does not show true speed, but rather speed relative to the radar unit. Look up “cosine effect”. A radar mounted off the side of the road is likely to read low and will be less accurate as you approach.

 

If this involves algebra that’s a hard pass.

 

My speedo is MORE accurate with the 265/70R17s than it was with the stock tires. At 70 mph it used to read 2 mph high. Now it reads 1 mph low.

 

Sold it. It was fun, until it wasn't.
It's never a good idea to restore a Daily Driver.
All my free time and weekend went into that car for almost 2 years.
I got burnt out and sold it.

There may be some pictures of it floating around somewhere.
My parents might have them. I took on this project in High School.
Sold it my senior year, and bought my first Tacoma. A 1996 Regular cab, 2.7 4X4.